It has been observed that many vehicles experience a chattering of their rear end leaf springs, when the van, truck, camper or automobile is started, in the forward or rear direction, especially while pulling a trailer or other load. The chattering of the leaf springs, which is also referred to as "spring windup", is caused by the backlash of the axle housing. At the start of vehicle moving under power, the rear axle begins to spin rapidly, causing the axle housing to rotate a few degrees against its mountings. The rotating housing causes pressure upon the leaf springs, which rapidly deflect, resulting in a chattering condition. The same condition exists with air or coil spring suspension.
The present invention reflects the discovery that a damping mechanism for damping the spring deflections can ensure a quieter start of the vehicle. The damping mechanism of this invention comprises a two-way, hydraulic, piston-cylinder unit. The unit is mounted to each rear end leaf spring via a pivotable bracket that is clamped about the spring. By changing the mounting brackets on the axle, the system can be used on air or coil spring suspension. The piston of the damping unit is attached at the pivotal end of the bracket. The damping mechanism is pivotally mounted to the frame of the vehicle via a clevis pin arrangement.
As the leaf springs are caused to deflect, the piston is caused to act against the fluid in the cylinder. The flow of the fluid is controlled at each port end of the cylinder by a solenoid-actuated cartridge valve. The solenoids are wired into the vehicle electrical system, and are each manually or automatically actuated by an electrical switch. The electrical switch is wired into the system so that the solenoid and cartridge valve is in a normally open position. Upon the deflection of the springs, a strain gauge, or optical sensor disposed upon each of the springs generates a signal to actuate the switch. The switch can also be actuated by sensing the speed of the drive shaft, a transmissional change from first gear, or a limit switch disposed upon the axle housing that senses the axle housing rotation. An optional small hole or orifice in the piston allows a gradual release of fluid in the cylinder, which may otherwise quickly damp the rapidly deflecting springs. The fluid flows to a reservoir and back to the cylinder under vacuum.